Turbine engines can be utilized for a number of purposes including propulsion and electricity generation. Because of the need to keep the turbine operating consistently with shortened periods of maintenance downtime, the state of the turbine engine art is constantly improving. To maintain the desired operating conditions in a turbine engine, one method of improving performance characteristics is by ensuring that the engine has sufficient combustion for operation.
In general, combustion flame in the combustion chamber of a turbine engine is facilitated by a series of fueled pilot nozzles which provide flame under pressure to the combustion chamber. Because of the volatile environment of the combustion chamber, i.e. extreme heat, pressure and vibration, unprotected pilot nozzles are subject to warping or clogging and the fuel passing therethrough is subject to coking. Such warping or clogging of the pilot nozzle results in a dramatic decrease in the efficiency with which the pilot nozzle operates as well as the combustion facilitated thereby.
Inefficient combustion results in a significant increase in operating costs in a number of ways, including increased fuel consumption, a loss in the amount of power the turbine produces and increased nitrogen oxide emissions. Nitrogen oxides (NOx) are classified as criteria pollutants by the EPA and are frequently created through high temperature combustion. Facilities releasing NOx emissions are required to obtain and hold permits. Facilities releasing greater amounts of NOx emissions than allowed under permit can be subjected to fines or additional permitting requirements, thereby increasing costs.
To reduce the amount of heat to which pilot nozzles are subjected, efforts have been made to protect the pilot nozzle by various cooling arrangements. These cooling systems can include water jackets or heat shields that surround the pilot nozzle to provide it protection from the volatile environment of the combustion chamber. These prior art heat shields generally have suffered a number of problems including fuel flow obstruction and air flow obstruction. Efforts have been made to remedy these defects by providing a pilot nozzle heat shield having flow jets and tangs. These tangs are concentrically angled inward and separated to provide improved fuel flow characteristics, resulting in an increase in combustion efficiency. The separated tang heat shield has been a significant improvement over prior cooling systems, however, this design too suffers a number of problems.
One major problem of the separated tang heat shield is due to a bending or warping of the individual tangs. Because of the high heat, pressure, and vibration in the combustion chamber, this volatile environment, coupled with the flow of the fuel through the pilot nozzle, causes the individual tangs to bend outward, or twist from their ordinary position, thereby changing the overall shape of the heat shield. The change in the shape of the heat shield results in a disruption of the fluid air flow through the heat shield as well as a disruption in the fluid flow of the pilot fuel from the pilot nozzle. Once distorted, the resulting effect is a decrease in reliability and efficiency, resulting in engine down time for heat shield replacement.
Because heat shields are in an environment of intense heat, pressure and vibration, when installed, they are welded onto the pilot nozzle. As such, the need to remove and replace a heat shield that has effectively changed shape and performance characteristics, requires the heat shield to be ground or milled from its mount and replaced. Such a process can increase the amount of maintenance downtime as well as the monetary costs associated with maintaining the turbine engine.